4x6L6 heater troubles

[EETStudent]

I am currently working on a AB763 twin reverb clone, and Ive run into some trouble with the heaters. I gave it a test run, and the only the first two power tube heaters fired it. The rest, including preamp tubes, did not. I suspected a bad connection between the pair of 6L6s, but that was not the case, as I read 6.7VAC all the way down the line with all tubes removed. I then tried the "non working" 6l6s by themselves in their same positions, all other tubes removed, and they did in fact fire up. The connections are good and the tubes are good. I installed the other set and suddenly they dont fire up again. I hope this makes sense. Any thoughts?

[Jazz P Bass]

Heater resistance

Measure the heater resistance of all the tubes.

[Enzo]

Your meter may measure voltage there with the tubes removed, but you can also measure AC voltage by grabbing the red probe with your fingers. I bet if you put the tubes in the sockets, the dark tubes would also have no voltage.

Your tubes sockets are wired with a pair of wires at each heater pin. One wire from the previous tube and the other wire to the next tube. Between your last hot 6L6 and the first cold one, one of the two wires between them is not completing its circuit.

Look at it, are the wires all in place? Now resolder BOTH heater pins on the last good socket, and resolder BOTH pins on the first cold socket. Did that fix it?

You can chase this down with a voltmeter with the tubes in place and power on. Or you can use an ohm meter with the tubes removed and power off. You can't use an ohm meter with tubes in.